1 files changed, 207 insertions, 0 deletions
diff --git a/pkg/sentry/fsimpl/devpts/devpts.go b/pkg/sentry/fsimpl/devpts/devpts.go
new file mode 100644
index 000000000..07a69b940
--- /dev/null
+++ b/pkg/sentry/fsimpl/devpts/devpts.go
@@ -0,0 +1,207 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package devpts provides a filesystem implementation that behaves like
+// devpts.
+package devpts
+
+import (
+	"fmt"
+	"math"
+	"sort"
+	"strconv"
+	"sync"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+// Name is the filesystem name.
+const Name = "devpts"
+
+// FilesystemType implements vfs.FilesystemType.
+type FilesystemType struct{}
+
+// Name implements vfs.FilesystemType.Name.
+func (FilesystemType) Name() string {
+	return Name
+}
+
+var _ vfs.FilesystemType = (*FilesystemType)(nil)
+
+// GetFilesystem implements vfs.FilesystemType.GetFilesystem.
+func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
+	// No data allowed.
+	if opts.Data != "" {
+		return nil, nil, syserror.EINVAL
+	}
+
+	fs, root := fstype.newFilesystem(vfsObj, creds)
+	return fs.VFSFilesystem(), root.VFSDentry(), nil
+}
+
+// newFilesystem creates a new devpts filesystem with root directory and ptmx
+// master inode. It returns the filesystem and root Dentry.
+func (fstype FilesystemType) newFilesystem(vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials) (*kernfs.Filesystem, *kernfs.Dentry) {
+	fs := &kernfs.Filesystem{}
+	fs.Init(vfsObj, fstype)
+
+	// Construct the root directory. This is always inode id 1.
+	root := &rootInode{
+		slaves: make(map[uint32]*slaveInode),
+	}
+	root.InodeAttrs.Init(creds, 1, linux.ModeDirectory|0555)
+	root.OrderedChildren.Init(kernfs.OrderedChildrenOptions{})
+	root.dentry.Init(root)
+
+	// Construct the pts master inode and dentry. Linux always uses inode
+	// id 2 for ptmx. See fs/devpts/inode.c:mknod_ptmx.
+	master := &masterInode{
+		root: root,
+	}
+	master.InodeAttrs.Init(creds, 2, linux.ModeCharacterDevice|0666)
+	master.dentry.Init(master)
+
+	// Add the master as a child of the root.
+	links := root.OrderedChildren.Populate(&root.dentry, map[string]*kernfs.Dentry{
+		"ptmx": &master.dentry,
+	})
+	root.IncLinks(links)
+
+	return fs, &root.dentry
+}
+
+// rootInode is the root directory inode for the devpts mounts.
+type rootInode struct {
+	kernfs.AlwaysValid
+	kernfs.InodeAttrs
+	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotSymlink
+	kernfs.OrderedChildren
+
+	// Keep a reference to this inode's dentry.
+	dentry kernfs.Dentry
+
+	// master is the master pty inode. Immutable.
+	master *masterInode
+
+	// root is the root directory inode for this filesystem. Immutable.
+	root *rootInode
+
+	// mu protects the fields below.
+	mu sync.Mutex
+
+	// slaves maps pty ids to slave inodes.
+	slaves map[uint32]*slaveInode
+
+	// nextIdx is the next pty index to use. Must be accessed atomically.
+	//
+	// TODO(b/29356795): reuse indices when ptys are closed.
+	nextIdx uint32
+}
+
+var _ kernfs.Inode = (*rootInode)(nil)
+
+// allocateTerminal creates a new Terminal and installs a pts node for it.
+func (i *rootInode) allocateTerminal(creds *auth.Credentials) (*Terminal, error) {
+	i.mu.Lock()
+	defer i.mu.Unlock()
+	if i.nextIdx == math.MaxUint32 {
+		return nil, syserror.ENOMEM
+	}
+	idx := i.nextIdx
+	i.nextIdx++
+
+	// Sanity check that slave with idx does not exist.
+	if _, ok := i.slaves[idx]; ok {
+		panic(fmt.Sprintf("pty index collision; index %d already exists", idx))
+	}
+
+	// Create the new terminal and slave.
+	t := newTerminal(idx)
+	slave := &slaveInode{
+		root: i,
+		t:    t,
+	}
+	// Linux always uses pty index + 3 as the inode id. See
+	// fs/devpts/inode.c:devpts_pty_new().
+	slave.InodeAttrs.Init(creds, uint64(idx+3), linux.ModeCharacterDevice|0600)
+	slave.dentry.Init(slave)
+	i.slaves[idx] = slave
+
+	return t, nil
+}
+
+// masterClose is called when the master end of t is closed.
+func (i *rootInode) masterClose(t *Terminal) {
+	i.mu.Lock()
+	defer i.mu.Unlock()
+
+	// Sanity check that slave with idx exists.
+	if _, ok := i.slaves[t.n]; !ok {
+		panic(fmt.Sprintf("pty with index %d does not exist", t.n))
+	}
+	delete(i.slaves, t.n)
+}
+
+// Open implements kernfs.Inode.Open.
+func (i *rootInode) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	fd := &kernfs.GenericDirectoryFD{}
+	fd.Init(rp.Mount(), vfsd, &i.OrderedChildren, &opts)
+	return fd.VFSFileDescription(), nil
+}
+
+// Lookup implements kernfs.Inode.Lookup.
+func (i *rootInode) Lookup(ctx context.Context, name string) (*vfs.Dentry, error) {
+	idx, err := strconv.ParseUint(name, 10, 32)
+	if err != nil {
+		return nil, syserror.ENOENT
+	}
+	i.mu.Lock()
+	defer i.mu.Unlock()
+	if si, ok := i.slaves[uint32(idx)]; ok {
+		si.dentry.IncRef()
+		return si.dentry.VFSDentry(), nil
+
+	}
+	return nil, syserror.ENOENT
+}
+
+// IterDirents implements kernfs.Inode.IterDirents.
+func (i *rootInode) IterDirents(ctx context.Context, cb vfs.IterDirentsCallback, offset, relOffset int64) (int64, error) {
+	i.mu.Lock()
+	defer i.mu.Unlock()
+	ids := make([]int, 0, len(i.slaves))
+	for id := range i.slaves {
+		ids = append(ids, int(id))
+	}
+	sort.Ints(ids)
+	for _, id := range ids[relOffset:] {
+		dirent := vfs.Dirent{
+			Name:    strconv.FormatUint(uint64(id), 10),
+			Type:    linux.DT_CHR,
+			Ino:     i.slaves[uint32(id)].InodeAttrs.Ino(),
+			NextOff: offset + 1,
+		}
+		if err := cb.Handle(dirent); err != nil {
+			return offset, err
+		}
+		offset++
+	}
+	return offset, nil
+}